Electrical winding.



E.V E. F. CREIGHTON.

ELECTRICAL wmDlNG.

APPLICAIIOK FILED NOV. 25, 1914.

Wltnesses: y Inventor:

QW/ 7% Elmer- EF. crei hton,

mum ssssssssssssssssssssssssssssssss n UMTED STATES PATENT oFFic ELMERE. F. CREIGHTON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF ANEW YORK.

ELECTRICAL WINDING.

roN, a citizen of the United States, residingr at Schenectady, county ofSchenectady, State of New York, have invented certain new and usefulImprovements in Electrical Vindings, of which the following is aspecication.

My invention relates particularly to trans former windings comprisingcoils arranged in groups.

The object of my invention is to so arrange and construct suchelectrical apparatus that the building upl 0f high voltages therein byabnormal frequencies is restrained and delayed.

It has been recognized that abnormally high frequencies, suoli as thoseproduced by .f

lightning, arcing grounds, etc., may give rise to disastrously highvoltages within an electrical winding, if there happens to be accessibleto the high frequency energy, a sufficiently large section of thewinding whose natural frequency or a harmonic thereof, is equal to theabnormal frequency; in other words, if there is accessible to the highfrequencya large section of the windingA in resonance therewith. Theenergy moving with the abnormal frequency may be little and the abnormalfrequency voltage at first, may be comparatively low, far froln adangerous value, but the continuous application of the high frequency tothe resonating section, causes greater and greater values of the energytherein to oscillate with the applied frequency, and the voltages torise 'accordingly to values dependent upon the length of time theresonating frequency is applied, the value of the energy in the section,and the damping and interference to which the oscillations aresubjected.

Prior to my invention, so far as I am aware, no attention whatever hasbeen paid in the design of any high power winding, to the naturalperiods of its various sections; the most common practice has been tomake and arrange all similar parts-of a winding, particularly the largersections, substantially alike, that is to make all the coilssubstantially alike and to compose all the groups of coils of the samenumbers of coils similarly placed, unless particular considerationsother than those relating to the natural periods of the sections,dictated other con- Specification of Letters Patent.

Patented July 4, i916.

Application filed November '25,1914, serial No. 374,068.

structions. In substantially each winding (of the type to which myinvention applies) made prior to my invention, therefore, the

various groups of coils thereof have ap l proximately the same naturalfrequencies, and if the resonating frequencyy of any group appearsanywhere on the system of which such a winding is a part, it is readilytransmitted to the other groups, even to the innermost part of thewinding, and all the groups resonate with it; occasionally a singlegroup of coils has shown a voltage higher than the normal voltage of theentire winding.

It is possible by my invention, to prevent, or at least delay thespreading of dangerous frequencies through those electrical windings towhich my invention relates and to restrain the dangerous oscillationthereof To this end I so construct and arrange the coil groups thereofthat the different groups have materially dierentv resonancefrequencies, so different that the frequency at which one grouposcillates can not readily pass over the other groups and can notreadily come into that group over them.

How far providing the different coil lgroups of the winding withdifferent natural frequencies is carried is immaterial tomy inventionexcept as herein indicated; in other words, the number of coil groups ofthe wihdings which are provided with different natural frequencies,their arrangement and the differences between their frequencies, aresubject to considerable variation according to the particular objects tobe accomplished, the size of the apparatus,

etc.

Preferably all the groups will have different natural fundamentalfrequencies and Vharmonics within the necessary limits as satisfactoryif only each two adjacent groups of the entire winding are of materiallydifferent periods or natural frequencies; Preferably, however, thelgroups (prof 'vidi'ng there are more thantwo groups in a giventransformer) will have'iiot less than three different naturalfrequencies. In differentiating the frequencies and harmonics it willprobably always be suflicient"`if the fundamentals and higher harmonicsvof the different groups are unequal below the eleventh harmonic; I am'inclined ,to believe that no frequencies greater' fthan.500,000 .cyclesper second .are dangerouszto electrical windings of the types nowcommon,- and hence that equalities of fundamentals and harmonics abovethis value are harmless ex'- cept as combining groups of such highnatural frequencies may result in a sectionof a lower and dangerousfrequency. With any two adjacent groups which resonate at about the samefrequencies, the greater the absolute difference between their twonatural fundamentals (or between twolvof their harmonics, or afundamental and a harmonic as the case may be), the greater is therestraint offered by one to the oscillation of the other; thus if onesection of a winding tends to oscillate at 85000 cycles per second,another section adjacent thereto offers more restraint to suchoscillation if.

its own natural frequency 'is 75000 cycles per second than it would ifits own natural frequency were 80000 cycles per second. It is notnecessary, however, that these differences be of eXtreme values, forsmall departures from the natural frequency of a group renders theenergy oscillations therein practically harmless; to certain coils ofnatural frequencies comparable with those often found in transformerwindings, I have applied frequencies live and one-half per cent. lowerand three per cent. higher than the natural frequencies and found thatthey resulted in voltages of only about twenty per cent. of the extremevoltage of the natural frequency, while frequencies ten per cent. belowand six per cent. above the natural frequency resulted in voltages, ofonly about twelve per cent. of the natural frequency voltage; forgreater departures from the natural frequency the voltages re= inainedsubstantially the same. Comparatively small restraints to the naturaloscillations, result therefore in considerable protection and willgenerally be sufficient to protect the windings.

I have illustrated in the accompanying drawing and hereafter described,two forms of transformers embodying my invention.

Figure 1 shows three coils about a coinmon magnetic core, one coil beingshown with separated turns, and the capacity relations of that coil andits parts being illustrated. Fig. 2 illustrates a disk coil transformer,the connections being shown diagrammatically.

The natural frequency of any group of coils of a winding dependssubstantially upon the relation between the inductance and capacity ofthat group of coils according to a law well understood: if either isincreased or rdecreased without a variation of the other, the naturalyfrequency or period of electrical oscillation -of that group is changedaccordingly. The object of my invention, therefore, may be accomplishedby providing the different groups. of coils of the windings withdifferent (and proper) ratios between their respective capacities andinductances.

The capacity and inductance of each portion ofl winding arel affected bya number of conditions. See Fig. 1 in which I have indicated .theprincipal features controlling the capacity of a coil; three windings 1,and y3 surround the common magnetic core 4. The winding Q has been shownwith open spaces so that the capacity relation between its turns may beillustrated. Between each two of the turns, for example between .theturns o and 6, there is a condenser action, representedhere by thecondenser 7. Between each of the turns and each of the adjacent coilsvthere is a capacity action as. representedy by the condensers S.Likewise, there is a capacity action, represented by the condenser S),between the coil or the turns as a whole', and each of the adjacentcoils, another represented by the condenser 10 between the turn 2G andthe core 1l, another between the coil as a whole and the core 4, whichis also represented by the condenser 10, anotherrepresented by thecondenser 27 between the turn 28 and the core 4, and still another,represented by the condenser 29, between the two sides of the coil, Eachcapacity action is affected by various conditions; by the spacing, theextent and shape and relative positions of the metallic surfaces, andthe material between the metal surfaces. In general the inductance ofany vpart of a windingA depends upon the number of turns in that part,the space between turns, the area circumscribed and the location of thatportion with respect to other' circuits. Thus the inductance of a giventurn depends upon the area circumscribed by that turn, its location withrespect to other turns and to its spacing from them; likewise, theinductance of a coil or group of coils depends upon the number of turnsin the coil oi group, their sizes, and their physical relation to eachother and to other circuits. These features are or will be understood bythose skilled in the art.

In carrying out my invention it is possible to secure the desireddifferentiation between tlie natural frequencies of the various groupsof coils by differentiating any or all of these features which controltheir capacities and inductances in a manner which 'will beundersto'odwithout further description (considering only one winding, though l myinvention may be embodied in both) the groups of coils and .21 arearranged to have unequal natural frequencies and higher harmonics belowthe eleventh harmonic.

This' may be done as pointed out above, by

giving due regard to one or any number of.

the features affecting the capacity and inductance of windings.- I havehere represented the result as accomplished, at least partly, by thediii'erences in the spacings of the coils. There are larger spacesbetween the group 21 and the coils' 23 and 24@ of the other winding,than, between the group 20 and its adjacent coils 24 and 25. It is, ofcourse, impossible to provide the groups of coils of the transformerillustrated with three periods, since there are but two groups,

, but were the number of groups greater than two, they should havepr`eferably not less than three natural frequencies of electricaloscillation. Not only should the natural frequencies of ,adjacent groupsbe differentiated as above, but also the natural .frequencies of a groupand an' adjacent nonsimilarv section should be differentiated whereversuch an arrangement mayvcontain sufficient energy to prove dangerousunder resonance conditions. Forl example, it is possible for the'coil 13to resonate with the group 20, or the coil l2 with the group 21, perhapsat the fundamental of the coil and an equal harmonic of the group; it ispreferable therefore to differentiate these sections if the coilscontain considerable en- So far inreferring to adjacent sections in .thedescription of specific embodiments of r,those sections of any apparatuswhich' are adjacent by reason of their direct', electrically conducting,connections; sections may also -be adjacent so far as my invention isconcerned, by reason of their electromagnetic connection, that isbecause of their mutually inductive relation, or by reason of theirelectrostatic relation, or by reason of any combination of'electrostatic, electromagnetic and electrically conducting relations.vention, any .two sections of electrical apparatus are adjacent, whichare so relatedto Within this broader idea of my in- 4 each other thatenergy may be transferred from one to the other.

While I have described the principle of my invention and the best mode Ihave contemplated for applying this principle, other modifications willoccur to those skilled in this art and-I aim in the appended claims tocover all modifications which do not involve a departure from the spiritand scope of my invention.

IWhat I claim as new and desire to secure by Letters Patent of the.United States.

1. In a transformer, a winding comprising a plurality of electricallyconnected coils assembled in groups and a second winding separating saidgroups, adjacent groups having unequal natural frequencies of electricaloscillation to restrain the building up `of dangerous voltages throughresonance.

2. In a transformer, a winding compris ing a plurality of electricallyconnected disk coils assembled in groups and a4 second windingseparating said groups, adjacent groups having unequal naturalfrequencies of electrical oscillation to restrain the building up ofdangerous voltages through resonance.

3. In a transformer, a winding comprising a plurality of electricallyconnected coils connected in groups and a secondary winding separatingsaid groups, adjacent groups having unequal natural fundamentalfrequencies of electrical oscillation and harmonies thereof to restrainthe building up of dangerous voltages through resonance.

4. In an electrical apparatus, a winding comprising a plurality ofelectrically connected-coils assembled in groups, 'one of said groupsand an adjacent coil having unequal natural fundamental frequencies ofelectrical oscillation and harmonics to restrain the building up ofdangerous voltages through resonance.

In witness whereof, I have hereunto set my hand this 23rd day ofNovember, 1914.

'ELMER E. F. CREIGIITON. IVitnesses:

BuNJAMiN B. HULL,

MARGARET E. VooLLiiY.

copies of thil patent may be obtained for ave cents each, by addressingthe Commiuloner o! Intent',

Washington, D. C.

